1. Field of the Invention
The present invention relates generally to the field of voltage amplifier circuits and more particularly to an improved broadband radio frequency (RF) voltage amplifier circuit for communication devices, which includes a resonant circuit used to provide enhanced voltage gain, and a method for boosting the voltage amplifier gain and input signal frequency range in such a circuit.
2. Related Art
Many of today's conventional complementary metal-oxide-silicon (CMOS) field effect transistor (FET) amplifiers obtain the needed high gain by using two stages of voltage amplification, with each stage comprising a pair of load devices, a differential pair of devices and a current source, or by using a single stage voltage amplifier having a pair of load devices, two separate pairs of cascade devices, a differential pair of devices and a current source.
Conventional voltage amplifiers, usable in phase-locked loops (PLLs) of communication devices, typically utilize a gm-R voltage amplifier stage, for example, comprising a cascade of voltage amplifiers. Conventional gm-R voltage amplifiers may be made with bipolar technology, and may have resistive load or active load. Such conventional voltage amplifiers work only at frequency roll-off and thus are not flexible. Therefore, they are impractical in circuits needing to provide large frequency range, such as PLLs of communication devices. Thus, some conventional voltage amplifiers are additionally equipped with an external LC circuit, which is used as a bandpass filter and can only accept input amplifier signals within a narrow frequency bandwidth.
Therefore, conventional voltage amplifier circuits typically have limited use in high gain operations in RF voltage amplifier circuits because they cannot satisfy wide enough frequency bandwidth requirement of these circuits. Accordingly, there is a need in the art for an improved RF voltage amplifier circuit which operates at high gain with low power consumption, usable in communication devices. There is also a need for a method for increasing voltage gain and frequency bandwidth of an RF voltage amplifier circuit usable in communication devices.